EFFECTS OF 2,4-D ON THE SIZE OF THE NAVEL-END OPENING AND FRUIT QUALITY OF ‘WASHINGTON’ NAVEL ORANGE

Large, protruding navel-end openings of navel oranges (Citrus sinensis (L.) Osbeck) are a major cull factor in the packhouse and make the control of some insects very difficult.
Previous work on navel orange trees suggested that the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), applied at full bloom at 20 mg·L^-1 reduced the diameter of the navel-end opening.
In a preliminary study to verify these results under South African conditions, similar results were obtained when 2,4-D was applied at 25 mg·L^-1 at petal drop on ‘Palmer’, ‘Robyn’ and ‘Lane Late’ navel orange trees.
To determine the optimal timing and concentration of application without any detrimental effects on fruit quality, 2,4-D was applied at 15, 25 or 35 mg·L^-1 at either full bloom or petal drop to ‘Washington’ navel orange trees in the following season. 2,4-D applied at full bloom significantly reduced the average navel-end size and increased the percentage of closed navel-ends, irrespective of the concentration applied.
In contrast, all petal drop applications had no effect on the average navel-end size or the percentage of closed navel-ends.
None of the treatments (full bloom or petal drop) affected fruit diameter, internal fruit quality, fruit colour, colour at the navel-end, pedicel diameter or creasing incidence significantly.
A weak relationship between fruit size and navel-end size was observed.
The data suggest that the application time of 2,4-D to reduce the size of the navel-end opening of navel oranges, seems to be more important for optimal efficacy than the concentration applied.

XI International Symposium on Plant Bioregulators in Fruit Production

J.S. Verreynne, G. Mupambi

Citrus sinensis, 2,4-dichlorophenoxyacetic acid, synthetic auxin, creasing, internal and external quality

https://doi.org/10.17660/ActaHortic.2010.884.101